Spotted this while setting up Microsoft Teams (Slack competitor).
You can sign up for a Microsoft Office 365 developer account free for 1 year, which gives you access to full Microsoft Office (including app downloads) for up to 25 users, with 5 app installs per user, Skype for Business, Sharepoint and Exchange email.
Obviously if you want to continue after a year there is a cost (£5.10 per user per month) but there's no cheaper way to get Office for a year... plus the tools to develop for things like Teams (my interest).
Potential value is therefore £1,530.
Not sure why HUKD is breaking the link, it's http://dev.office.com/devprogram